Re: [RFC] Start SMP subsystem earlier

On 1/5/15 8:18 AM, Hans Petter Selasky wrote:
> Hi,
> 
> There is a limitiation on the number of interrupt vectors available when
> only a single processor is running. To have more interrupts available we
> need to start SMP earlier when building a monotolith kernel and not
> loading drivers as modules. The driver in question is a network driver
> and because it cannot be started after SI_SUB_ROOT_CONF due to PXE
> support I see no other option than to move SI_SUB_SMP earlier.
> 
> Suggested patch:
> 
>> Index: sys/kernel.h
>> ===================================================================
>> --- sys/kernel.h    (revision 276691)
>> +++ sys/kernel.h    (working copy)
>> _at__at_ -152,6 +152,7 _at__at_
>>      SI_SUB_KPROF        = 0x9000000,    /* kernel profiling*/
>>      SI_SUB_KICK_SCHEDULER    = 0xa000000,    /* start the timeout
>> events*/
>>      SI_SUB_INT_CONFIG_HOOKS    = 0xa800000,    /* Interrupts enabled
>> config */
>> +    SI_SUB_SMP        = 0xa850000,    /* start the APs*/
>>      SI_SUB_ROOT_CONF    = 0xb000000,    /* Find root devices */
>>      SI_SUB_DUMP_CONF    = 0xb200000,    /* Find dump devices */
>>      SI_SUB_RAID        = 0xb380000,    /* Configure GEOM classes */
>> _at__at_ -165,7 +166,6 _at__at_
>>      SI_SUB_KTHREAD_BUF    = 0xea00000,    /* buffer daemon*/
>>      SI_SUB_KTHREAD_UPDATE    = 0xec00000,    /* update daemon*/
>>      SI_SUB_KTHREAD_IDLE    = 0xee00000,    /* idle procs*/
>> -    SI_SUB_SMP        = 0xf000000,    /* start the APs*/
>>      SI_SUB_RACCTD        = 0xf100000,    /* start racctd*/
>>      SI_SUB_LAST        = 0xfffffff    /* final initialization */
>>  };
> 
> This fixes a problem for Mellanox drivers in the OFED layer. Possibly we
> need to move the SMP even earlier to not miss the generic FreeBSD PCI
> device enumeration or maybe this is not possible. Does anyone know how
> early we can start SMP?

We need a lot more work before this is ready.  This is one of the goals
of the multipass new-bus stuff.  In particular, we have to enumerate
enough devices to bring event timer hardware up so that timer interrupts
work so that tsleep() will actually sleep.  In addition, we also need
idle threads created and working before APs are started as otherwise
they will have no thread to run initially.  This is certainly a desired
feature, but it is not as simple as moving the sysinit up I'm afraid.

-- 
John Baldwin